The top priority for the Steelers: finding a way, any way, to beat the visiting San Diego Chargers on Sunday and avoid a dreaded 1-3 start for the first time since the 2006 season.

What may be a close second is restoring the swagger to a defense that has been unmasked in the fourth quarter, dating to the Super Bowl in February.

In the Steelers' past four games, opposing quarterbacks have completed 73 percent of their throws in the final 15 minutes and combined for four touchdown passes.

The Steelers' inability to make a defensive stand in the fourth quarter is a big reason why they have squandered late leads in losing their past two games. And a beleaguered pass defense doesn't exactly get a bargain in Sunday's nationally televised game.

"We know we can be in games, but right now we don't know that we can win them," Steelers free safety Ryan Clark said. "We have to fix that."

They'll likely have to do that, at least in the short term, without All-Pro strong safety Troy Polamalu.

Polamalu has missed the past two games with a sprained left knee, and there are no indications the five-time Pro Bowler will be healthy enough to play against the Chargers.

His absence has changed the complexion of a unit that ranked No. 1 in the NFL last season in passing and total defense. Clark, however, refused to use Polamalu's loss as a crutch or a rationalization for what happened late in the game in Chicago and Sunday in Cincinnati.

"We miss him, don't get me wrong, and I think he's the best at his job, but we can go out there and make those plays," Clark said. "When we were No. 1 last year, it was because 11 guys played really good football."

That group returned largely intact this season, and they have played well through the first three quarters of games.

The last 15 minutes have been a different story, as 27 of the 50 points the Steelers have allowed this season have come in the fourth quarter.

The Bengals scored 14 fourth-quarter points Sunday. The final eight came when Carson Palmer directed a 16-play, 71-yard drive that was capped with a 4-yard touchdown pass to Andre Caldwell with 14 seconds left. Palmer converted the ensuing 2-point conversion with another completion in the end zone, this one to Brian Leonard.

"We knew we were going to score," Bengals wide receiver Chad Ochocinco said. "Carson said, 'When we score, we are going for two.' That's all I can remember. I was thinking that we were nowhere near the goal line."

Palmer may have spouted such bravado to inspire confidence in his teammates. But he had every reason to be confident, and it showed as he twice converted on fourth down, including once when the Bengals needed 10 yards to keep their drive alive.

Palmer's performance left a proud defense humbled and a bit bewildered.

"It's still early, but when you have a game (won) and you don't come away with the game you tend to start looking at yourself like, 'What's going on?' " said Tyrone Carter, who has been starting at strong safety in Polamalu's place. "We need to find answers. We just can't find a way to make plays and get off the field."

The Steelers have not forced a turnover in the fourth quarter this season. Their pass rush also has been lacking at a time when they need it most.

Such reality has led to questions about whether the defense is showing its age. The Steelers started six players who are over 30 years old against the Bengals.

The Steelers, to a man, dismissed such a notion. But they also acknowledged they have to stop teams from converting on third and fourth down.

"We strive to be a great defense. We strive to make those plays," defensive end Brett Keisel said. "If we don't start making them, it's going to be a long year."